Glossary Cryptography and payment
Atomic swap
Also: atomic swaps, cross-chain atomic swap
Origin: The cross-chain atomic-swap protocol was described by Tier Nolan on the Bitcoin Talk forum in May 2013; the first Bitcoin–Litecoin atomic swap was completed by Decred and BarterDEX teams in 2017.
A cross-chain exchange of cryptocurrencies between two parties such that both legs of the swap complete or both fail — with no intermediary holding the funds. Constructed using hash-time-locked contracts on each chain, with a shared hash pre-image binding the two transactions.
Reviewed
An atomic swap is a cross-chain exchange of cryptocurrencies between two parties such that both legs of the swap complete or both fail — with no intermediary holding the funds. The construction uses hash time-locked contracts on each of the two chains, with a shared hash pre-image binding the two transactions: the receiver of one leg can claim it only by disclosing a pre-image that the other party then uses to claim the matching leg on the other chain. If either party fails to act within the time window, the corresponding HTLC expires and the original sender reclaims the funds.
The protocol was first described in operational terms by Tier Nolan on the Bitcoin Talk forum in May 2013. The first publicly-completed cross-chain swap — between Bitcoin and Litecoin — was executed by the Decred and BarterDEX teams in 2017. The mechanism has since been generalised: Bitcoin–Ethereum swaps run through the COMIT framework; Bitcoin–Monero swaps run through the Farcaster and COMIT XMR projects; and the original Bitcoin–Litecoin and Bitcoin–Litecoin/Dogecoin pairings remain operationally simple because both chains use compatible script primitives.
The privacy property atomic swaps procure varies with the chain pair. A Bitcoin–Monero swap (in either direction) routes the privacy-relevant leg through Monero’s default-private transaction surface — a buyer can acquire Bitcoin on a KYC exchange and convert to Monero via atomic swap without the swap counterparty learning the buyer’s identity. The on-Bitcoin leg remains visible to chain analysis, but the on-Monero leg is unlinkable from the on-Bitcoin one beyond the timing correlation a sophisticated analyst could attempt.
Atomic swaps are one of the operational paths the publication recommends for acquiring Monero without going through a KYC exchange — alongside P2P exchanges like Bisq, AgoraDesk, Hodl Hodl, and RoboSats. The Monero payment dossier sets out the operator’s view; OffshorePress’s payment routes themselves do not involve atomic swaps directly, but the subscriber’s acquisition path may, and the operator’s policy is to describe the acquisition options honestly without endorsing any particular service.